JP3060828B2 - Tracking control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a consumer digital VTR for recording / reproducing a compressed video signal using a rotary magnetic head, and more particularly, to information for variable speed reproduction at an arbitrary speed higher than normal reproduction. The present invention relates to a tracking control method suitable for performing variable-speed reproduction of magnetic tape recorded in a distributed manner at each track position according to a scanning locus of a head.

[0002]

2. Description of the Related Art In a consumer digital VTR, an image compression technique is used to reduce the amount of data recorded on a magnetic tape. As an example of the image compression technique, a so-called M
The PEG method is generally used.

In the MPEG system, a video is constructed using a difference between frames. Therefore, if high-speed reproduction is performed at a speed different from normal reproduction, the continuity of data of the preceding and succeeding frames is lost. You cannot composite video from.

[0004] For this reason, as a variable-speed reproduction method of a VTR utilizing image compression by the MPEG system, for example, "FIRS"
T SCAN TECHNOLOGY FOR DIGITAL VIDEO TAPE RECORDERS
(IEE Transactions on Consumer Electronics Vol.3
9, No. 3, AUGUST 1993) ”.

In this method, a variable speed reproduction is performed at a specific position on a magnetic tape which matches a scanning locus of a reproduction head corresponding to the tape speed of the variable speed reproduction so that an image can be decoded even at a variable speed reproduction. The video data for reproduction is recorded separately and separately, thereby enabling variable-speed reproduction such as search and shuttle reproduction even on a tape recorded by compression in the MPEG system.

FIG. 5 shows an example of a track pattern on a magnetic tape recorded by the above-described method at 3 × speed and 9 × speed in the forward (forward) direction (the head configuration is 180 ° facing 1).
Channel). In the figure, reference numeral 41 denotes a reproducing head, a shaded portion such as 42 is a region where video data for triple-speed reproduction is recorded, and a hatched portion such as 43 is a video for 9-times speed reproduction. The area where data is recorded, 44 is the rotating magnetic head 4 during normal reproduction.
Reference numeral 1 denotes a scanning locus, and 45 and 46 denote scanning locuses of the rotating magnetic head 41 during 3 × and 9 × speed reproduction, respectively.

In triple speed reproduction, the head scans three tracks diagonally as indicated by a locus 45 in FIG. Therefore, in order to perform the triple speed reproduction, the data 42 for the triple speed reproduction is divided and recorded at a specific position of each of the three tracks in accordance with the scanning locus of the rotary magnetic head 41, and similarly. , 9
In the double speed reproduction, the rotating magnetic head 41
Scans across nine tracks, so that the data 43 for 9 × speed reproduction is divided into nine tracks and recorded.

Each track is composed of a plurality of data blocks of several hundred bytes, and each data block records a block address including a track number and a block number together with image data. .

By the way, in the above-mentioned method, since the video data for variable speed reproduction is recorded only on a specific track which matches the head scanning trajectory, it goes without saying that the normal reproduction state shifts to variable speed reproduction. When the speed is changed in the variable speed playback state, the scanning phase must be controlled so that the rotating magnetic head accurately scans the predetermined track on which the video data is recorded. No.

In a consumer VTR or the like, the control of the scanning phase of the head with respect to the recording track is generally performed by relatively controlling the running speed of the tape (the rotation speed of the capstan motor).

FIG. 6 shows a simplified servo block configuration of a capstan motor for performing variable speed reproduction of a tape recorded in the pattern shown in FIG. In the figure, 1 is a capstan motor, 2 is a motor speed detector (fv converter), 3 is a control amplifier, 4 is a motor drive circuit, 5 is an integrator, 6 is a system control circuit. Reference numeral 7 denotes a phase detector for detecting an error in the number of scanning tracks relative to a track on which variable speed reproduction data is recorded, 8 a phase detector for detecting a tracking error from a head reproduction signal, 9 a switching circuit, and 10 a control. An amplifier, 11 indicates an adder, and 12 to 14 indicate comparators.

The phase detector 7 detects, for example, a block address of reproduced data from a reproduced data string, and a block address table in which the original variable speed reproduced data is recorded. Are compared to calculate the deviation between the current scanning track and the desired variable speed reproduction track, and output an error signal according to the scanning track number error and the error direction.

Hereinafter, the tracking control of the variable speed reproduction by the apparatus shown in FIG. 6 will be described.

When a variable speed reproduction command key (not shown) is operated by the user, the system control circuit 6 recognizes the key and switches the switching circuit 9 so that the contact point of the switching circuit 9 becomes the position a in FIG. At the same time, the command speed for variable speed reproduction is identified and input to the speed detector 2.

Thus, the control of the rotation speed of the capstan motor 1 is started so that the tape playback speed becomes the variable speed playback speed specified by the system control circuit 6, and the tape speed does not operate with the phase control. Speed control loop
It is started up to a predetermined speed only by the step.

Next, when the tape traveling speed reaches a predetermined speed, the system control circuit 6 detects this from the motor speed, and switches the contacts of the switching circuit 9 from a to b in the figure, ie, the phase detector 7 Switching circuit 9 to supply output to control amplifier 10
Control. At this time, since the phase control was not operating,
At the moment when the contact point of the switching circuit 9 is switched to b in the figure, the scanning locus of the head does not always scan the recording track of the variable speed reproduction data as shown in FIG. It will be.

Therefore, if the scanning locus of the head deviates from the desired track at the moment when the contact point of the switching circuit 9 is switched to b, an error signal corresponding to the deviation amount and direction is sent from the phase detector 7 to the control amplifier 10. The error signal becomes zero by the phase control by the phase control loop A, that is, the phase pull-in control is started so that the head scans the desired track.

Next, when the head scanning phase reaches one track before the desired phase, this identification signal is output from the phase detector 7 to the system control circuit 6. When the system control circuit 6 recognizes this, the contact signal of the switching circuit 9 is output. B to c, that is, the switching circuit 9 is controlled to switch the control signal of the control amplifier 10 from the output of the phase detector 7 to the output of the phase detector 8.

The phase detector 8 is provided with an area division A which is well-known, for example, in a DAT (digital audio tape recorder).
It is configured using TF and the like, and outputs an error signal corresponding to the off-track amount and off-track direction of the head with respect to the recording track.

Therefore, after the contact of the switching circuit 9 is switched to c, the phase control loop B performs phase pull-in control based on the error signal of the phase detector 8, and thereafter the scanning locus of the head is sequentially changed to a desired one. The center of the track on which the variable speed reproduction data is recorded is scanned.

[0021]

In the variable speed reproducing operation using the tracking control device shown in FIG. 6, the access speed until the rotating magnetic head scans a desired track depends on the phase error of the track number. This is pull-in control. Assuming that the variable speed reproduction speed is N, the recording pattern as shown in FIG. 5 requires a phase pull-in of a maximum of ± N / 2 tracks. Therefore, it is important to reduce this time as much as possible.

That is, the variable speed reproduction data is recorded only on a specific track, and is used when shifting from the normal reproduction state to the variable speed reproduction, or when changing the speed in the variable speed reproduction state. Since the video data cannot be reproduced until the rotating magnetic head scans the desired track, it is desired that the desired track can be quickly scanned from the viewpoint of improving the quality of the reproduced image.

However, the tracking device of FIG. 6 has a drawback that the access speed cannot be so high.

Hereinafter, this point will be described.

In the block diagram of FIG. 6, the transfer function of the system (the phase response characteristic of the head with respect to the step input) H when the track number error is introduced by the phase control loop A is represented by the following equation (1).
(S), in which the DC gain is represented by γ, the response frequency band of the system is represented by ωn, and the damping coefficient of the speed control system is represented by ζ.

[0026]

(Equation 1)

In the specific implementation of the tracking device shown in FIG. 6, the damping coefficient ζ is generally designed to be one or more which is a critical condition in consideration of the stability of the system and the like.
Table 1 shows a design example of each parameter when ζ is set to about 2 as a specific example.

[0028]

[Table 1]

FIG. 7 is obtained from Equation 1 when the variable speed reproduction speed is set to 27 times under the parameter design conditions in Table 1 and a step input of 27/2 tracks which is the maximum phase pull-in error is given. 4 shows the time response characteristics of phase pull-in. The time required for the rotating magnetic head to converge within one track with respect to the track on which the 27-times speed video data is recorded is about 0.5.
It takes 2 seconds, during which time the 27 × speed video data cannot be reproduced and the video is interrupted, resulting in an unsightly state.

An object of the present invention is to solve the above-mentioned problems and quickly pull in a predetermined track when switching from normal playback to variable speed playback, or when changing the speed in variable speed playback. An object of the present invention is to provide a tracking control device capable of improving the quality of a reproduced image at the time of shifting to variable speed reproduction.

[0031]

According to the present invention, there is provided a damping coefficient control means for controlling a damping coefficient of a tape running speed control. The damping coefficient 速度 of the speed control is made different before and after reaching one track before the variable speed reproduction track.

That is, since the system stability is not required in the phase pull-in process of the track number error, a control structure is adopted in which the damping effect of the speed control system is weakened during this period and the phase pull-in response is accelerated.

[0033]

The damping coefficient 速度 of the speed control system is set to 1 or less until the scanning phase of the rotary magnetic head reaches one track before the track on which variable speed reproduction data is recorded by the damping coefficient control means. As a result, the damping effect of the speed control is weakened, the maximum speed of the capstan motor is increased, and the response of the phase pull-in is increased.

After the scanning phase of the rotary magnetic head reaches one track before the track on which the variable speed reproduction data is recorded, the damping coefficient control means sets the damping coefficient 速度 of the speed control system to one. With the above setting, the damping action of the speed control is strengthened, the scanning phase of the rotating magnetic head converges to the target phase stably, and the tracking of the rotating magnetic head is performed in a state where the stability of the system is secured.

[0035]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a tracking control device according to the present invention. In FIG.
Is a damping coefficient control means for switching the value of the damping coefficient の of the speed control system. Other parts denoted by the same reference numerals as those in FIG. 6 indicate the same or equivalent parts, and the operation is also the same.

First, the configuration and operation of the damping coefficient control means 15 different from the conventional tracking control device shown in FIG. 6 will be described.

The damping coefficient control means 15 operates to switch the gain according to a command from the system control circuit 6. FIG. 2 shows an example of the specific configuration.
1 is a changeover switch, and 32 is an attenuator of gain K.

When the phase control loop B is selected for the phase control at the time of normal reproduction or variable speed reproduction, the system control circuit 6 switches the contact of the changeover switch 31 to the A side, and controls the phase control at the time of variable speed reproduction. When the phase control loop A is selected, a control signal is output so that the contact of the changeover switch 31 is switched to the B side.

The damping coefficient control means 15 is a cascade element of the speed detector 2, and switching this gain means switching the value of the damping coefficient に as can be seen from equation (1). That is, when the changeover switch 31 is connected to the contact A and the gain is high, the damping coefficient ζ
When the changeover switch 31 is connected to the contact B side and the gain is low, the damping coefficient 作用 acts to be small.

Therefore, when the value in the state where the damping coefficient 大 き い is large is set to about 2 as in the conventional example of FIG. 6 and the value in the state where the damping coefficient 小 さ い is small is set to 0.5, for example, the attenuator 32 The gain K is designed to have a value of 1/4.

In the following, the entire operation of the configuration shown in FIG. 1 will be described by taking a 27 × speed variable speed reproduction as an example and the gain K of the attenuator 32 of the damping coefficient control means 15 as an example.
Will be described with reference to FIGS. 3 and 4.

In FIG. 3, reference numeral 47 denotes an area in which video data for variable speed reproduction at 27 × speed is recorded, and reference numeral 48 denotes a trajectory of the magnetic head 41 scanning the video data 47 for 27 × speed reproduction at 27 × speed reproduction. It is shown.

When a 27-times speed reproduction command is input, first, the system control circuit 6 recognizes this and controls the switching circuit 9 so that the contact of the switching circuit 9 is at the position a in FIG. The speed detector 2 identifies the command speed of reproduction and
Enter As a result, the rotation speed of the capstan motor is increased by the speed control loop so that the running speed of the tape becomes 27 times that during normal reproduction. At this time, the system control circuit 6 controls the damping coefficient control means 15
So that the contact point of the changeover switch 31 is connected to the A side.
The damping coefficient control means 15 is controlled.

When the tape speed reaches 27 times the target speed, the scanning phase of the rotary magnetic head is changed by the phase control loop A to 48 as shown in FIG.
At the same time, the contact of the changeover switch 31 of the damping coefficient control means 15 is switched from A to B by a command from the system control circuit 6.

As a result, when the track number error is pulled in by the phase control loop A, the gain of the speed control loop is increased as shown in FIG.
Since the damping effect of the speed control system is weakened, the maximum speed of the capstan motor is increased, and the response of the phase pull-in is reduced. The system works to be faster.

FIG. 4 shows that the speed damping coefficient ζ is set to about 0.5.
6, the phase control loop A has 2
This is a time response characteristic of phase pull-in calculated from Equation 1 when a step input of 27/2 tracks, which is the maximum track phase error of 7-times speed reproduction, is given.

The time required for the rotating magnetic head to converge within one track with respect to a predetermined track on which video data for 27 × speed is recorded is about 0.04 sec, which is about 0.2 sec of the characteristic shown in FIG. On the other hand, it is reduced to about 1/5.

Next, when the scanning phase of the rotary magnetic head is pulled within one track of the desired phase by the phase control loop A, the system control circuit 6 recognizes the control signal from the phase detector 7 and contacts the switching circuit 9. Is switched from b to c in the figure, and the phase control is switched to the phase control loop B, and at the same time, the changeover switch 31 of the damping coefficient control means 15 is switched.
The damping coefficient control means 15 is controlled so that the contact point (A) is connected again from the B side to the A side. As a result, the gain of the speed control loop is in its original high state, that is, the damping coefficient 速度 of the speed control is set to a value of 1 or more, so that the damping action of the speed control is strengthened and the scanning phase of the rotating magnetic head is controlled by the phase control. The phase control by the loop B stably converges on the target phase, and the tracking of the rotating magnetic head is performed in a state where the stability of the system is secured.

The embodiment of the present invention has been described above. In the embodiment, the variable speed reproduction in the forward (forward) direction has been described as an example, but this is not particularly limited, and the variable speed reproduction in the reverse (reverse) direction or the variable speed reproduction at an arbitrary speed is possible. Needless to say, reproduction can be similarly developed. Also, an example in which the gain of the speed control loop is switched with respect to the control of the damping coefficient 示 し has been described, but this is not particularly limited. For example, the gain of the phase control loop and the control amplifier Needless to say, it is possible to change the gain or the like. Further, the switching of the damping coefficient ζ may be performed only when the rotating magnetic head is within a range close to the track on which the video data for variable-speed reproduction is recorded. It is not necessary, and the switching is not limited to one time, and it is of course possible to perform control such that the switching is performed a plurality of times, and various modifications can be easily made without changing the gist of the present invention.

[0051]

As described above, according to the present invention,
In variable speed reproduction tracking control of a magnetic tape in which information for variable speed reproduction at an arbitrary speed higher than normal reproduction is dispersedly recorded at each track position according to the scanning locus of the rotating magnetic head, scanning of the rotating magnetic head is performed. The value of the damping coefficient の of the speed control system is set to 1 or less until the trajectory reaches the close range of the track on which the video data for variable speed reproduction is recorded, and thereafter, the value of the damping coefficient ζ is set to 1 or more. Since the switching control is performed, the scanning phase of the rotating magnetic head can be quickly pulled into a predetermined track when shifting from the normal reproduction state to the variable speed reproduction, or when changing the speed in the variable speed reproduction state. In addition, it is possible to realize a tracking control device capable of improving the quality of a reproduced image at the time of shifting to variable speed reproduction.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of the present invention.

FIG. 2 is a specific configuration diagram of a damping coefficient control unit of FIG.

FIG. 3 is a diagram showing a scanning locus of the rotating magnetic head in the embodiment of FIG.

FIG. 4 is a diagram showing a time response characteristic of a track phase pull-in in the embodiment of FIG. 1;

FIG. 5 is a diagram showing an example of a recording pattern of variable speed reproduction information.

FIG. 6 is a diagram showing a conventional tracking control device.

FIG. 7 is a time response characteristic diagram of the pull-in of the track phase by the device of FIG. 6;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Capstan motor, 2 ... Speed detector, 3, 10
... Control amplifier, 4 ... Capstan drive circuit, 6.
..System control circuits, 7, 8 phase detectors, 9 switching circuits, 11 adders, 12, 13, 14 comparators, 15 damping coefficient control means, 31 ... changeover switch, 32 ... attenuator, 41 ... rotary magnetic head

Claims (2)

(57) [Claims] An oblique track is formed on a magnetic tape to record information for normal reproduction, and information for variable speed reproduction at an arbitrary speed higher than that of normal reproduction corresponds to a scanning locus of a rotating magnetic head. An apparatus for reproducing magnetic tapes recorded at specific positions of respective tracks, wherein the high-speed running control means causes the magnetic tape to run at a speed higher than a normal reproducing speed, and the rotary magnetic head is adapted to perform the variable speed reproduction. Phase control means for performing phase control so as to scan a track on which information for recording is recorded, and at the time of variable-speed reproduction of the magnetic tape, the high-speed running control means causes the magnetic tape to run at a predetermined speed at a high speed. At the same time, a track wherein the phase control means controls the scanning phase of the magnetic head to a predetermined track position on which information for variable speed reproduction is recorded. And a damping coefficient control means for controlling a damping coefficient of a tape running speed control. In a phase pull-in control of the magnetic head in the variable speed reproducing operation, a scanning phase of the magnetic head is controlled for variable speed reproducing. A tracking control device for controlling the damping coefficient control means so that a damping coefficient of the tape running speed control is different before and after reaching a predetermined position before a track phase in which information of the tape is recorded. . 2. The damping coefficient of the tape running speed control by the damping coefficient control means is set to 1 until the scanning phase of the magnetic head reaches a predetermined position before a track phase in which information for variable speed reproduction is recorded. 2. The tracking control apparatus according to claim 1, wherein the control is controlled to one or more thereafter.